Development of a pneumatic damping approach for wire tension control in micro wire electrical discharge machining

Abstract

This study addresses the technical bottleneck of wire tension control in micro wire electrical discharge machining (micro w-EDM) by proposing an original pneumatic damper design capable of stabilizing the tension of a 20 μm-diameter brass wire and improving machining stability and precision. Conventional mechanical and magnetic tension-control mechanisms often suffer from friction, hysteresis, and backlash effects when applied to micron-scale wires, resulting in unstable wire feeding and dimensional inaccuracy. The developed pneumatic damping approach generates both axial and circumferential damping forces through controllable chamber pressure. A mathematical model relating chamber pressure to wire tension was established and integrated into a precision wire-cut EDM platform. Experimental results indicate that a chamber pressure of 1.6 MPa consistently produces a wire tension of 43.2 gf, corresponding to a minimum kerf width of approximately 24 μm and a unilateral discharge gap of only 2 μm. Under an optimal discharge capacitance of 200 pF, an average kerf width of 23.74 μm, a standard deviation of 0.43 μm, and a surface roughness of Ra 0.63 μm were achieved. A feed-rate of 0.04 mm/min yielded the lowest discharge short circuit ratio (DSCR), enhancing process repeatability. Further, validation of the machined slanted-tip microprobe array and spiral microstructures demonstrated highly consistent morphology in SEM analyses, with kerf width error below 1 μm and slope deviation within 0.005. These results confirm that the proposed pneumatic damping approach provides stable vibration absorption and precise tension control, significantly improving the machining quality of nonlinear microstructures and offering a significant advancement in micro wire tension control technology.